In the field of information transmission, error correction decoding is generally used in order to reduce the influence of errors occurring in a transmission path as much as possible, and to carry out highly reliable information transmission. This error correction decoding controls errors by appending redundancy code to the information code. In an actual signal transmission system, because the amount of redundancy code that can be appended is limited by such factors as the scale of the hardware etc., in the case where transmission data errors have occurred exceeding the error correcting capability possessed by redundancy code, erroneous data will be received. To cope with this type of situation, a method has been adopted where error detection codes such as CRC (Cyclic redundancy check) are appended to information that is not permitted to have transmission errors, and the existence of uncorrectable transmission errors is detected at the receive signal side.
However, an inferior transmission path, such as is often the case in radio communication, the possibility of the occurrence of transmission errors beyond the correction capability possessed by the code is comparatively high, and there is a need for more powerful error correction codes. On the other hand, in order to improve the error correcting capability it is generally necessary to increase the redundancy code included in the code, but this is not possible in a signal transmission system in which the transmission efficiency can not be sacrificed.